Fatigue-creep design of transpiration cooled nickel gas turbine blades via low order aerothermal-stress and crystal plasticity finite element modelling

Abstract

Transpiration Cooling (TC) systems can substantially improve the fuel efficiency of jet engines by allowing them to run much hotter than current designs allow. However, TC systems require radically new designs where large cyclic thermomechanical stresses and creep-plastic deformation can limit the life of core components. This can only be mitigated through integrated design approaches which simultaneously consider the aerothermal and mechanical performance. We develop here a low order aerothermal-stress model (LOM) which combines first order coolant flow and fluid-solid convective-conductive heat transfer calculations with stress calculations in the solid. The LOM provides rapid answers to crucial design questions: how much cooling air and how many cooling holes are required in gas turbine blades for them to operate safely at a given turbine inlet (hot gas) temperature? The LOM also narrows the range of conditions under which Crystal Plasticity Finite Element (CPFE) simulations may be required for fatigue-creep life assessment at final design stages. Our answer to previous pessimistic views on the practical use of TC is that TC systems can actually work thanks to the threefold benefit of cooling holes in reducing metal temperatures, temperature gradients and effective thermal stresses. CPFE simulations confirm this new conclusion, encouraging the wider use of our hybrid design strategy in turbomachines, hypersonic technologies and fusion reactors as well as the take-up of TC systems to deliver durable hydrogen-fuelled turbines for Net Zero.